UNITED STATES DEPARTMENT OF THE INTERIOR
STEWARTL. UDALL, SECREI'ARY
********
BUREAU OF RECLAMATION FLOYD E. DOMINY, COMMISSIONER R. J. PAFFORD JR., REGIONAL DIRECTOR
REGION 2
********
SAN LUIS UNIT CENTRAL VALLEYPROJECT, CALIFORNIA
GEOLOGY AND GROUND-WATER RESOURCES DEFINITE PLAN APPENDIX
Sacramento, California
February 1963
. ' GEOLOGY AND GROUND-WATER RESOURCES SAN LUIS SERVICE AREA
The geology and ground-water studies were made and this appendix was prepared by the Regional Geology Branch, WilJ1am I. Gardner, Chief. This work was performed under the supervision ot Hibbarcl E. Richardson by William R. Cooke, assisted by Carl W. Roots, David c. Magleby and others ot the Geology Branch statt, both 1n the present study and in the earlier stages ot the geohydrological study ot the groand-water reservoir.
i
SAN WIS SERVICE AREA GlOOI.OGY AND GROUND-WATER RESOURCES • Definite Plan Appendix TABLE OF CONTENTS Pye No. Sl:JlllilARY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • l INTROWC'?ION •••••••••••••••• •·• •••••••••••••••••••••••••• 7 Location and Extent •••••••••••••••••••••••••••••••••• 7 Acknowledgements••••••••••••••••••••••••••••••••••••• 8 General Description•••••••••••••••••••••••••••••••••• 8 Climate ••••••••••••••••••••••••••••••••••••••••••• 8 Phy-si.ograplJ¥ •••••••••••••••••••••••••••••••••••••• 8Soils·••••••••••••••••••••••••••••••••••••••••••••• 10 Basic Data ••••••••••••••••••••••••••••••••••••••••••• lOPrevious work ••••••••••••••••••••••••••••••••••••• 10 Ground-water records •••••••••••••••••••••••••••••• l3 Well-numbering s,rstem ••••••••••••••••••••••••••••• l4 Geologic Setting and History ••••••••••••••••••••••••• 15 GROUND-WATER G]!X)LOGY •••••••••••••••••••••••••••••••••••• 17 General •••••••••••••••••••••••••••••••••••••••••••••• 17 Upper Zone ••••••••••••••••••••••••••••••••••••••••••• 17 Corcoran Clay l8 Lower Zone ••••••••••••••••••••••••••••••••••••••••••• ··················~····················· 19 Nonwater-Bearing Formations •••••••••••••••••••••••••• 20 GROUND-WATER CONDITIONS ••••••••••••••••••••••••••••••••• 2l Source ••••••••••••••••••••••••••••••••••••••••••••••• 2l Occurrence ot Ground Water ••••••••••••••••••••••••••• 21 Upper zone •••••••••••••••••••••••••••••••••••••••• 2l Lower zone •••••••••••••••••••••••••••••••••••••••• 2l Depth and Movement ••••••••••••••••••••••••••••••••••• 22 Upper zone •••••••••••••••••••••••••••••••••••••••• 22 Lower zone •••••••••••••••••••••••••••••••••••••••• 2.3 Water-level Fluctuations ••••••••••••••••••••••••••••• 2.3 Upper zone •••••••••••••••••••••••••••••••••••••••• 2.3 Lower zone •••••••••••••••••••••••••••••••••••••••• 24 Qualit7 ot Ground Water•••••••••••••••••••••••••••••• 25 General ••••••••••••••••••••••••••••••••••••••••••• 25 Upper zone ·····················~·················· 25Lower zone •••••••••••••••••••••••••••••••••••••••• '2T
ii
CONTENTS (Cont.) Page No. GROUND-WATER UTILIZATION••••••••••••••••••••••••••••••• 29 Ground-Water Pumpage • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 29 Well Characteristics • • • •.• • • • • • • • • • • • • • • • • • • • • • • • • • • • 30 Present Cost ot Pumping••••••••••••••••••••••••••••• 32 GROOBD-WATER SUPPLY, Present Conditions.;.............. 35 General••••••••••••••••••••••••••••••••••••••••••••• 35 Increments•••••••••••••••••••••••••••••••••••••••••• 35 Compaction of lower-zone sediments••••••••••••••• 35 Lower-zone subsurface inflow trom the east....... 37 Deep percolation f'rom gross demand••••••••••••••• .38 Interzone exchange••••••••••••••••••••••••••••••• Percolation ot westside stream flows............. 39 .39 Upper-zone subsurface in.f'low .f'rom the east••••••• 40 Unditterentiated recharge•••••••••••••••••••••••• 40 Gain in storage•••••••••••••••••••••••••••••••••• 40 Decrements••••••••••••••••••••••••••••••••••••••••••· 41 Ground-water pumpage, lower zone••••••••••••••••• 41 Ground-waterpumpage, upper zone••••••••••••••••• 41 Interzone exchange••••••••••••••••••••••••••••••• 41 Subsurface outflow •••• ~•••••••••••••••••••••••··~ 41 Overdraft••••••••••••••••••••••••••••••••••••••••••• 42 Sate Ground-Water Suppl1' •••••••••••••••••••••••••••• 42 GROUND-WATER SUPPLY; Ultimate Project Conditions••••••• 44 General • • • • • • • • • • • • • • • • • • • • • • • • •.• • • • • • • • • • • • • • • • • • • • 44 Increments•••••••••••••••••••••••••••••••••••••••••• 44 Decrements•••••••••••••••••••••••••••••••••••••••••• 46 Ground-water pumpage, lower zone••••••••••••••••• 46 Ground-water pumpage, upper zone••••••••••••••••• 46 Outnow to drains................................ 46 Sate Ground-Water Suppll' •••••••••••••••••••••••••••• 47
iii SAN WIS SERVICE AREA TABJ.ES Table No• Page No. l. . Average cost ot water trom. lowe:r-sone irriga­tion wells, 1960 conditions-Westlands Water District•••••••••••••••••••••••••••• 33 2. Average cost ot water tram lower-sone irriga-tion wells, 1960 conditions-area outside ot Westland.a Water DJ.strict 1n the San Luis Service Area•••••••••••••••••••••••••••••• 34 Average annual water suppq inventor;y tor~ Luis Service Area-Period 1950 through 1960 Average annual water suppq inventor;y and sate ground-water suppq {pumpage)-ultimate project conditions•••••••••••••••••••••••· 45 PLATES Plate No. l. Ground-water contours-depth 1961 and change 1951-61, lower wate?'-bearing sone. 2. Location .map, u. s. B. R. drilling program, upper zone. Generalized e1evation and depth contours-top ot Corcoran clq. Ground-water profile A-A•. 5. Ground-water elevations, lower water-bearing zone, spring 1951. 6. . Ground-water elevations, lower ·water-bearing zone, spring 1961. 7. Water level hydrographs, upper zone. iv The service area of the San Luis Unit contains about 610,500 acres in the central-west side or the San Joaquin Valley, California (plate 1).
This ground-water report presents the physical and chemical characteristics of the ground-water reservoir and the estimates of safe ground.;.water supply (pumpage) for the service area. The purpose is to determine the average annual supplemental ~rt requirement frcm the San Luis Canal tor ultimate phases of developnent of the service area. For water contract purposes, the ground-water study and analTsea has been divided into two subareas; one for Westlands Water District and another for the area outside or the District. The ground-water reservoir has been divided into an upper zone above the Corcoran clay aquiclude and a lower zone below the clay. The sate ground-water supply (pumpage) under project conditions was determined on the basis ot a water supply inventoey £or the period 1950 through 1960 by eliminating an undesirable recharge item (water derived from canpaction or lower zone sediments), and r~by making an adjust­ment
for a greater amount of percolation due to a larger gross demand and project conveyance l~ases. The safe ground-water supply (pumpage) under project conditions is as follovs: Westlands
Outside of
Sate Ground-water
Water
Westlands
San Luis
Supply Cpumpage>
District
Water District (acre-feet}
Service Area
Lower zone Upper ~one
225,000§7.000
65,000 86.000
290,000173.000
TOTAL
312,000
151,000
46.3,000
Nearq all the local supply in the San Luis Service Area is from ground water and it will continue.to be important under project condi­tions. The ground-water reservoir is an accumulation or sediments or varying permeabilities and a maximum thiclmess or nearly .3,000 feet. The water-bearing sediments consist of coalescing alluvial ran deposits laid down by Coast Range streams and or sediments rrom the Sierra Nevada which were washed westerly beyond the present valley axis and are interlayered with the Coast Range alluvium to considerable depth beneath the valley-floor. The Coast Range type sediments are predomi­nantly fine-textured, ill-sorted, and yield less ground water than those from the Sierra Nevada which are mainly well sorted and coarser.
A relatively impervious layer called the Corcoran clay occurs at depths or 200 to 800 feet below the ground surface. '.!'his lake-bed deposit effectually divides the ground-water reservoir into two distinct parts--an upper water-bearing zone and a lower water-bearing zone. The upper water-bearing zone is ccmposed of Coast Range and Sierran sedi­ments with interconnected pervious beds and the ground water is uncon­fined to semiconfined, although some confinement has been noted in the
2
deeper Sierran sediments above the Corcoran cl.a)". Sierran-derived sediments below the Corcoran cla7 are major aquifers in geohydrologic continuit7 with aquifers underl1ing the east side of the San Joaquin Vallq. Water below the Corcoran cla7 in the lower water-bearing zone is under artesian head. Approximateq 85 to 90 percent of the total ground-water pumpage is estimated to now came from this deep zone.
Initialq, ground-water movement in both the upper and lower zones was eastward toward.a the vallq trough. At present, the semi.­perched water table, occurring over much of the service area, generalq has an eastward gradient. Water in the Sierran sands qing just above the Corcoran cla7 along the eastern boundar,' now has a westward gra­dient. In the lower zone increased pumpage, especialq since 1945, has reversed t_he gradient. During the base period (195~1960) ·the piesometric slope has averaged about 20 feet per mile toward the west along the eastern edge or the service area.
Depths to water range tran less than 10 feet tor the semiperched water table ot the upper sone to more than 700 feet to the piezanetric surface ot the lower zone (plate 1).
Upper zone semiperched water level measurements in recentq drilled Bureau teat holes indicate that the water table baa risen as much as 40 feet since 1952. Water levels in the lower portions ot the upper zone appear to be static or declining slightq. The average lower zone piezcmetric .surface dropped about 80 to 85 feet f'ran 1943 to 1951 and an additional 100 teet rrcm 1951 to 1961.
Upper zone water quality varies both laterally and vertica~. Water in the semiperched portion ot the upper zone is genera~ ot very poor quality with high total dissolved solids (TDS)•. Water quality improves with depth trom about 300 feet to the top or the Corcoran clay', averaging about 1,500 ppn total dissolved solids. However, sodium chloride waters averaging 5,000 ppn TDS occur in the basal portion ot the upper zone in an area mostq outside the service area along the trough frail Mendota to Helm. In the area around Five Points where heavy upper zone pumping occurs, water or 1,000 ppn TDS is found in the Sierran sands inmediateq overl1'ing the Corcoran clay. Native waters in the lover sone are f'airq constant, genera~.& sodium·sul­tate type with TDS ot about 800 ppn. However, very few wells produce water soleq !'rem the lower zone. Most of the wells in the service area yield a blend of' upper and lower zone waters with the total dissolved solids averaging 1,200 ppn.
All but minor amounts of' water used in the service area is derived frcm ground-wat~r pumpage and is estimated to be 697,0<XJ acre-feet per year tor the base period. or this amount 485,0<XJ acre-feet represents pumpage in Westlands Water District. or the total pumpage, sane 600,000 acre-feet per year canes fran the lower confined. zone.
4
\,~,·
r- '"\
~
Wells are drilled almost exclusively b7 rotary-methods to depths ot 1,000 to .3,000 feet, averaging about 1,500 feet. ·They are can­pletely caaed and gravel packed with perforations in the casing trom 100 or 200 teet above the Corcoran clay to the bottan. In this manner both the upper and lower ground-water aone• are tapped and yield about 1,100 gallons per mlnute.
Present replenishment ot ground-water supplies is a total ot several sources: a) recharge from compaction ot lower-sone sediments, b) aubsurtace inflow to the upper and lower zones tram the east, c) deep percolation trom gross demand, .and d) percolation tram west-side stream fl.on. Rain.tall ia uaual.17 80 light that it does not penetrate beyond the root zone in significant quantity.
Subsurface intlow to the service area averaged about 220,000 acre-feet annualq tor the base period 1950-1960 and will be maintained under project conditions. It has been estimated that .32,000 acre-feet anuallf of westside stream tlows percolates to ground water. Theretore, about 252,000 acre-feet is the long-term average annual ground-water supply tram natural sources to the service area.
At the present time, an undesirable means ot recharge occurs fran the ccmpaction and loss ot pore water from sediments below the Corcoran clay, due to the lowering ot the hydrostatic pressures in the lover zone. Thus, the present annual overdraft is .310,000 acre-feet. This type ot compaction which results in surface subsidence in the area,
J
5 will cease under project conditions when pmnping in the lover sone 1• reduced to the sate ground-water suppl.T.
6 IHTRODCJCTIOH
Location and Ext.ent
The San Luis Service Area or the San Luis Unit, encompassing 610,500 acres, is located on the west side or the San Joaquin Valley, California 1n western Fresno County and adjacent parts ot Merced and Kings counties to the north and south respective~. Its eastern boundary roughl.T parallels the topographic trough ot the Valley. The western bound&r7 lies near the base ot the Coast Range f'oothills. The service area has a north-south length of' about 65 miles and an east-west width ot 13 miles. It includes all of' the Westlands Water District of' approximatel1' 391,000 acres and portions ot the Westplains Water Storage District, Broadview, Panoche, and San Luis water districts amounting to approx1matel1' 219,500 acres. Plate l shows the location of' the service area and its relationship to the San Luis Unit.
The entire San Lu1s Service Area is underlain by ground water. For water contract purposes, the ~d-water study and ana~sis of the service area has been divided into two sub-areas; the area within the Westlands Water District and the area outside or the District. The boundaries of' the sub-areas are shown on plate l, and will be subse­quent~ described 1n detail.
Towns within the service area are: Mendota, Five Points, and Huron. Also situated within the area is the large United States Naval
7 Base at Lemoore. The center or the service area is about 30 miles
southwest or Fresno. The valley is served by State Highwa1s 33, 41,
180 and 198 as well as the Southern Pacific Railroad.
Acknowledgements
Thia stud)" has made extensive use ot"basic ground-water data, studies and reports ot others. Appreciation is expressed eepecialq to United States Geological Survey-. Acknowledgement is also due to private companies, irrigation districts and individuals for basic data furnished and tor allowing access to their property tor drilling and other purposes.
General Description
Climate.--Average annual precipitation amounts to about seven inches, 90 percent occurring between the first ot November and the last ot April. The average temperature range is trca about 80 degrees 1n J~ to .about 45 degrees in January. Max1Jllum and minimum tempera­tures ot 116 degrees and· 14 degrees, respectiveq, have been recorded. See Hydrology Appendix for greater details.
Phzsiographz.-The San Joaquin Valley is the southern portion of the great Central Valley of California. It is bounded by the Sierra Nevada on the east, the Tehachapi Mountains to the south, the Coast Ranges on the west, and the Sacramento-San Joaquin River Delta and
, drainage divide on the north. Its length is about 250 miles and its width is as great as 55 miles with an average of 35 miles.
8 The principal drainage outlet ot the vall.e," is the San.Joaquin River which rises in the Sierra Nevada northeast ot Fresno and flows general.l1' southwesterly to the vicinity ot Mendota in the valley trough where it turns abruptl.1' to the northwest and tlows thence into Suisun Bay. The southern halt ot the valley, blocked by deposits ot the Kings River and Loa Gatos Creek fans, drains to the interior basins except tor periods ot tlood nows when some ot the Kings River flows reach the San Joaquin by way ot Fresno Slough, a natural overflow channel.
The main ephemeral streams ot the Coast Range flow northeastward toward the valley trough. In the service area thq are: Little Panoche, Panoche, C&ntua, and Los Gatos (also lmown as Arroyo Pasaajaro) creeks. The .flows ot these streams are intermittant and seldom reach the trough with the water being absorbed by the alluvial f'an deposits.
The west side of the valley is a low, gently northeasterly sloping plain formed by the broad, coalescing alluvial rans or the Coast Range. In the service area the elevation ranges frail about 200 feet along its eastern edge to about 485 feet along the western border. These fans ext.end to as nmch as 18 miles from the. .foothills with slopes-or 20 to .30 .feet per mile in their more active apical portions, flattening valleyward to less than .five feet per mile. Relief on the plain is very small except for the incised stream channels which
are obliterated valleyward by land leveling for farming.
9
Soils.-The soils or the area are mainly clasai.f'ied as vall97 land soils. These are deep Coast Range alluvial ran, calcareous, soils; the lower portion or the tans formed under high water table conditions are saline and alkaline. Soil descriptions, locations, and relation to crops are presented in the Agricultural Land Use Appendix.
Basic Data
Previous work.-Rererence material used in this study is listed below:
Date or
Agenc,:
Title or Report
Report
United States Geological Surv97
Water-supply Paper 222, Prelimi­naey Report on the Ground Waters or San Joaquin Valley,
1908
California.
United States Geological Survey
Water-Supply Paper 398, Ground Water in San Joaquin Valley, California.
1916
United States
San Luis Unit, Local Water
1954
Bureau or Recla-
Resources Appendix
mation
United States Geological Survey
Water-Supply Paper 1360-G, Ground-Water Conditions in the Mendota-Huron Area, Fresno & Kings
1957
Counties, Calif'ornia.
United States Geological Survey
Water-Supply Paper 1469, Ground­water Conditions and Storage Capacity in San Joaquin Valley-, California
1959
10 During 1950 to 1953 acme 67 core holes were drilled and
laborato:ry studies made ot samples theretran in the San Joaquin
Vallq. Four holes were drilled tor the earlier San Luis investiga­tion
and were either partia~ or ccmpleteq cored to depths ranging
f'ran 527 teet to 1,500 feet. In each, electric logs were run and
individual tubes set in individual aquifers, trcm which water samples
tor analysis were drawn and in which periodic wate~level measures
have been made.
The laborato:ry studies included the identif'ication or the specific source of' the materials. encountered in order to dif'te~ entiate the extent or individual tans, which bear directl)" on ground­water migration and availability-. Using petrologic and mineralogic ana11"ses or spot samples taken from or near the active channel of several major streall8 as a guide, diagnostic concentrations ot cer­tain of the cannon minerals, or the ratios between them, were worked out tor the tine and very tine sand components of' core samples. Other laboratory tests involved the physical and chemical characteristics ot the sediment samples.
Several agencies including the Bureau of' Reclamation, Geological Survey, and the State Division of' Water Resources cooperated in an interagency subsidence study ot the San Joaquin Valley. As a part of' this study acme deep core holes nre drilled, sampled, electric logged and compaction recorders installed. Three of these holes are in the San Luis Service Area.
11
The State Division o.f' Water Resources also core-drill.ed some holes in the service area which were sampled in part.
After review ot the above data, it became apparent there is onl.7 a small amount o.f' data conceming the hydraulics and water quality or the ground-water bodies overlying the Corcoran clay. The question concerning the hydraulics and water quality o.f' the ground­water bodies over11'1ng the Corcoran clay. The question concerning the dependability or the upper water-bearing zone to serve as a partial source or supply, as well as drainage problems could not be resolved with the existing data.
An initial program or seven core holes 100 to 200 feet deep were drilled and cored in the .f'all o.f' 1961 by the Bureau. These holes indicated that a much expanded drilling program was needed,and work was started on this program earl.1' in 1962. Th6 first phase ot the en­larged program consisted ot 40 auger holes, 10 to 95 feet deep, can­pleted to the water table, if possible, and cased for future water level measurements. At present they are being measured monthly. Samples were taken for moisture content, chemical analysis, and mechanical analysis. In addition a water sample was taken for chemical analysis. (See plate 2 for location of these holes.)
To further understand the geohydrologic characteristics ot the upper water-bearing zone, some 42 core holes are being drilled adjacent to the augerholes to 50 feet or more below the water table. These
12
holes are completed and sampled the same as the auger holes except
that the perforations are general.:cy-onl1' in the lower portion or the
hole. Some 34 ot these holes had been completed by' March 1, 1963.
(See plate 2.)
.To obtain water quality and water levels 1n the Sierran sands above the Corcoran clay, six core holes will be dr11led to the clay. These holes are to be electric logged in addition to the sampling stated abo,re. In completion or these holes, the casing will be perforated on]J in the deep Sierran sands iDmediately above the Corcoran clay.
In addition to the above program, 18 core holes drilled tor the preconstruction investigation of ~he San Luis C&nal have been ut1l11ed. These holes have been cored, sampled, and water level measurements are being made monthl1'.
All or these holes have been drilled along 10 genera~ northeast­southwest trending sections. Cross sections are being constructed to show the general geo~ologic properties of the sediments, water quality, and moisture content.
Ground-water records.--Water-Supp~ Paper 398 includes water level meaaurements and data for 72 wells in the west side area. These wells were measured in 1907 and earlier, and included several deep wells. A report tor the Boston land~ contained static and pumping water level measurements shown by one shallow and one deep zone map and were drawn f'rClll 1925 data.
Pump test records, made by the Pacific Gae and Electric ca.pan;y are dated as ear~ as 19.33 and are continuous. These are probabq the
t
best long-term water level records tor the area. Onl,-a few owners
made these records available to the Bureau.
The Bureau or Reclamation ground-water records date from 1939. The observations trom 1939 to 1944 are very meager; those trcm 1944 to 1948 are good, numbering 200 to 900 a year; 1948 to 1950 records are eparae; observations tor 1950 through 1952 number about 1,000 a year; and observations since 1952 are rather meager. Measurements or the semi.perched zone and upper zone were started in 1962 on sane 90 Bureau test and ground-water observation holes.
.,
The Geological Survey began measurements in late 1950 and have measured every year since then some 200 to 700 wells.
The State of California Division ot Water Resources has made measurements in the area since 1957, most~ during the f'all or the year.
Well-numbering gstem.-Wells have been numbered according to the public land system of rectangular co-ordinates. The letter-number
14
well identification units designate, in order, the township, range, section, and 40-acre tract within the section. The last number designates the sequence in which the well was canvassed within each 40-acre tract. The section aubdivision is shown below.
D
C
B
A
E
F
G
H
M
L
K
J
N
p
Q
R
Geologic Setting and Histor;r
The San Joaquin Valley occupies the southern part of the Great Valley structural trough, a vast downwarped basin ot deposition filled with thouaancta ot teet ot sedimentary materials ranging from Cretaceous to Recent in age. The east aide ot the valley is bounded by the Sierra Nevada, a westward-tilted block, chief'q ot granitic and metamorphic rocks, which dips westward under the sedimentary materials ot the valley. Rising more rapidl.3r on the west side ot the valley and closer to the service area, is the Coast Range ot c<>mplex]Jr folded and faulted Mesosoic and Tertiary strata. The Tertiary formations are elastic
15
strata_ot both continental and marine origin. The Mesozoic sedi­ments include great thicknessee or marine Cretaceous sandstone and shale, and variabq metamorphosed elastic and volcanic rocks or the Franciscan formation (Jurassic ? ) which rorma the core or the range.
The Cretaceous and the Tertiar;r marine formations which outcrop in the Coast Range underlie the valley at depth in a broad asyme­trical S1Dclinal told, whose steep limb is on the western side. During the late-Tertiary-, the Coast Range emerged as a high integrated land
C
mass, and the San Joaquin trough became, and has remained, an interior valley. In the late-Tertiary and Quaternary age, water-bearing conti­nental sediments were deposited on the expansive floor of the valley chiefq as alluvial ran and floodplain deposits, but aJ.so in lake beds during wetter periods. Some deformation in the Coast Range and bordering western part ot the valley has continued into Quaternary' so that the older continental Tertiary and Pleistocene beds are tilted and exposed in terraces and low foothills on the western edge or the valley.
'
.· .Lb
. GROUND-WATER GEOLOGY
General
The ground-water reservoir underlies the entire San Luis Service Area. The water-bearing sediments consist or both Coast Range and Sierra Nevada material. In this study the ground-water reservoir has been divided into an upper aone above the Corcoran cia,. aquiclude and a lower zone below the clay.
Upper ?.one
The upper zone includes sediments dawn to the Corcoran clay which are derived trm both the Coast Range and the Sierra Nevada. Thick­neaa ot this zone ranges to 800 feet (See plate .3). Surface deposits in the service area are Recent alluvial deposits derived primaril.7 trcm the Coast Range except tor a small portion alol}8 the eastern edge or the service area where Recent deposits of the Kings River occur. The upper sone sediments are Pleistocene and Recent 1n age.
Sierran sediments, consisting general.l1' of tine to medium well sorted sands and silts, extend up to nine miles west ot the eastern bound&r7 of the service ~a. These sediments are predom:lnantly fioodplain deposits ot the San Joaquin and Kings rivers which inter­finger with Coast Range material. This Sierran material is readily recognized by the abundance ot micaceous granitic fragments. The Sierran deposits exhibit a greater permeability than those of the
17
-
Coast Range. Since the source or these sediments are the Sierra Nevada, there is bydrologic continuity with aquifers to the east of the service area. There is also limited interconnaction with overlying Coast Range materials.
Irrigation wells completed in the upper zone Sierran deposits yield good quality of water to many wells along the eastern boundary or service area from north of Five Points to west of Lemoore. Average well yields are about l,000 gallons ·per minute. Elsewhere, many deep sone wells are perforated opposite the more permeable strata of the upper zone. From Mendota to Helm along tbe trough the micaceous sands in the upper zone contain water of inferior quality for irrigation.
The Coast Range alluvial deposits in the upper zone consist of highly lenticular beds of poorly sorted clay, silt and sand with an occasional bed or well-sorted sand and gravel. The coarser grained sediments occur on the higher portions ot the west-side fans. The Coast Range deposits are ot moderate permeability, generally recharged from west-side streams and by deep percolation of irrigation water. In some wells the Coast Range aquifer material of the upper zone is tapped by perforations in the well casing.
Corcoran Clay;
The Corcoran clay is a widespread body of diatomaceous clay and silt averaging 60 to 80 feet thick and found at depths to 800 feet. It underlies most of the service area. This clay, since it is
18
relatively impervious, has great hydrologic significance as it divides the gro,.md-water reservoir into two major zones, the confined lower zone and the unconfined or genera~ poorly confined upper zone. The Corcoran clay is believed to be Pleistocene in age and was formed in a great fresh water lake which covered much of the San Joaquin Valley. Ot.her workers believe it may be late Pliocene. Its structure and areal extent are shown on plate 3.
!e(er Zone
This zone is of great importance in the service area as it supplies an estimated 85 percent or more of the present ground-water pumpage. Aa mentioned above, it is effectively confined by the Corcoran cla:, except locally west or Huron. Much of the water now being produced from this zone is due to water released by compaction ot lower zone sediments. The base of the lower zone is not well defined but is considered to be the first occurrence of saline water. It is 1,000 to 3,000 feet below the ground surface. Maey deep wells in the service area perforate opposite the more permeable strata of the upper zone and in this manner, due to head differences, there is some intersone exchange between the upper and lower water bearing
zones.
Like the upper zone, sediments of this zone consist genera~ ot tine-grained Coast Range material inter.f'ingered with more permeable coarser grained granitic sands ot the Sierra Nevada. The latter
19
sediments yield most ot the ground water. Thus, again there is
lateral hydrologic continuity with Sierran materials to the east
as well as llmited vertical continuity between east and west-side
source materials.
Genera~, the lower sediments are referred to as the Tulare formation or Pliocene and Pleistocene age. The west-side Sierran sediments are.probab~ correlative with the east-side Kern and Friant formations.
Non-gter kring Fomations
The none-water bearing formations range in age from· Jurassic to Pliocene and underlie the ground-water reservoir. These formations outcrop in the foothill areas adjacent to the valley floor. The formations are large~ marine sandstones and shales containing poor quality or water. GROUND-WATER CONDITIONS
Source The source of ground water in the service area is at present
I
from water derived from the canpaction of sediments (subsidence),
subsurface inflow from the east and northeast from the percolation
or pumped ground water, and percolation from imported and natural
surface waters. All of these sources except percolation of pumped
ground water represent a supply' of new water to the area.
Rainfall in the area is of such low magnitude that recharge does not generally occur from this source.
Occurrence of Ground Water
Upper zone.-Ground water in the upper zone is found under various types of conditions, but in this report is grouped into two general types. The upper-most water in the service area is a semiperched water body. Below this semiperched body, but above the Corcoran clay, ground water is found in varying amounts ot confine­ment. In general, however, this zone is treated as being semiconfined and, thus, there is some degree of hydraulic interconnection of aquifers.
Lower zone.--The lower zone represents the ground-water reservoir below the Corcoran clay and is considered to be confined throughout the service area. However, locally west or Hllron where the Corcoran
21
clay is missing, there is some indication of recharge from the surface and thus, semiconfined conditions tor this portion of the service area are indicated.
Depth and Movement
· Upper zone.-The existence of a shallow, semiperched water table over the eastern half or the service area has been better defined by a recently conducted and partiall3' completed Bureau of Reclamation drilling program. Depth to this semi.perched body ranges from less than 10 feet near the eastern edge of the service area to more than 40 feet in the central part of the service area. Initially, all ground-water movement in upper and lower zones was from the west toward the valley trough to the east. The present gradient of the semiperched water table generall3' slopes toward the east; fran a northwest-southeast trending line approximatel.1' near the center of the service area the gradient appears to be westward. (See plate 2 and Drainage Appendix, plate 2.)
Geohydrologic data indicates that the water body existing in sands lying at depth above the Corcoran clay is semiconfined. In this zone thin beds of clay and silt impede vertical movement of water. Depths to water in aquifers above the clay are on the _order of 60 to 100 feet in the eastern portion of the service area; however, only a few wells of this type have been measured and control is poor. Meager water level measurements indicate the semiconfined water table
22
has a westward gradient in the Sierran sands along the eastern edge of the service area.
As mentioned previously, the Bureau drilling program will supple­ment existing upper zone data so that the relationship of ground-water bodies can be better interpreted.
Lower Zone.-Depth to the piezometric surface of the confined system below the Corcoran clay ranges from around 150 feet along the eastern edge or the service area to more than 700 feet in the western portion. Average depth to the piezometric surface in 1961 was about 400 feet. (See plate l.) Prior to World. War I, it is believed that the piezometric surface had a gently sloping, northeasterly gradient. Since that time, due to increasing ground-water draft on this zone, it now has induced a reversed gradient. Plate 4 shows the position of the piezometric surface for the years 1906, 1943, 1951, and 1961, and also the large magnitude of decline in piezometric surface as ground-water use has expanded. Elevation contours for the spring of 1951 (plate 5) and 1961 (plate 6) show ground-water movement to be toward the west at a gradient of about 20 feet per mile through thick Sierran aquifer :material. This has also been the average gradient for the last ten years along the eastern border of the service area.
Water-Level Fluctuations
Upper zone.-Long-term records are not available for water-level fluctuations in the upper zone. Indications of a rise in the semiperched
2.3 zone come from comparing recently drilled shallow Bureau holes, 1961 through 1963, with a generalized depth to water map presented in the u. s. G. s. Water-Supply Paper l.li.69, for the 1952 shallow water table. This map, although the best available, is o~ approxL­mate in many locations due to the lack or good control. At some locations apparent rises or five to more than 40 feet have been noted. These rises are apparently due to irrigation return flow •
.
Sane locations also indicate a lowering of the water table.
The piezometer pipes installed in the Bureau test hole l5/14-15E are good indicators or what is genera~ o_ccurring in the upper zone. Pipes were set within the following intervals; 0-280 feet, 300-460 feet, and 480-700 feet. The Oto 280-foot interval shows that water levels in this part of the upper zone have risen more than 20 feet since 1950. Interval 300 to 460 feet indicates that water levels have remained fairly stable except for seasonal fluctuations due to pumping. The 480 to 700-.foot water levels show a slight de­cline during the period of record and large magnitude or seasonal fluctuations which probably indicate nearby wells are tapping this zone. (See plate 7.)
Lower zone.--Lower-zone fluctuations of the piezometric sur­face are much better defined. In U. s. G. s. Water Supply Paper 398, plate 1 outlines an area of flowing artesian wells in the San Joaquin Valley for the year 1905. A portion of this outlined area is within ..
the service area. Since the end ot w·orld 'tlar I, the piezometric surface has declined due to greater and greater use of ground water for agriculture. Average elevations of the piezometric surface for a ntUnber of years have been determined from contour maps or the lower zone. The average elevation in the spring of 1943 of the service area was about 69 feet above sea level; by the spring of 1951, it had dropped to 13 feet below sea level. Water levels continued to decline and by 1961 they .had dropped to ll4 feet below sea level'or an average decline of about 10 feet per year. Wells in western portion of the service area have been declining on the order of 15 feet per year. Pl.ate l shows lines of equal change of the piezometric surface of the lower zone for the period 1951 through 1961.
9Balit;t of Ground Water
General.~Most ot the irrigation wells 1n the service area are perforated 1n the upper and lower zones and the chemical nature of water from a given well depends upon its perforated interval. The character of water in the upper and lower zones is described in some detail in the U. s. G. s. Water Supply Paper l,360-G. The Bureau has obtained considerable data in the past year primarily for the shallow portion of the upper zone.
Upper zone.-Ground waters in this zone contain high concentra­tions of sulfate salts. Chemical changes in the upper-zone waters occur latterall.y such as along the eastern portion of the area where
25
waters from the eastside and westside commingle; gradational changes al30 occur with increasing depth.
Chemical analy'ses of water samples taken from Bureau holes drilled to a few feet below the water table, generally in the eastern half or the service area and within 75 feet or the ground surface, indicate that north of Bureau holes 807, 806, and 821 and south of holes 827, 828, and 829, the waters are generally of the sodium sulfate type (See plate 2). The area between these holes has water of the calcium-magnesium-sulfate type. The Drainage Appendix presents the chemical analy'ses or water from these shallow holes and sane from deeper holes in the upper zone drilled thus far. The total dissolved solids (TDS), of these waters less than 75 feet deep, ranges from 1,145 parts per million (PJ:!ll) to 51,250 ppn, averaging around 12,000 pt:m, with the sodium percentage ranging from 20 to 90. From the limited deeper holes, completed ·to date, it appears that the water quality improves with depth. Water quality from 75 to 200 or .300 feet below the land surface is still a rather moot question. The U.S. G. So in Water-Supply Paper l.360-G, .frail rather limited data, reports
most or the waters in the upper 200 to .300 feet are of the calcium and magnesium sulfate type with the sum of the determine constituents averaging about .3,000 ppn with a sodium percentage or .35 •. From this, it appears that the water below 75 feet is of better quality. The water of poor quali~y in the eastern half or the service area within 75 feet of ground surface presents, serious threat to the ground-water
26
--:
supply above the Corcoran clq under present conditions ot operation. Under project oonditiona with drains over the lower halt ot the service area and water ot ver17 good qualit7 being imported, water quality will improve in this part of the upper zone.
The chemical character ot the water in the upper zone trom 200 to 300 teet below land surface to the Corcoran c~ shows consider­able lateral variance. These waters show a decrease in total deter­mined constituents to about 1,500 ppm and an increase in sodium to about 55 percent. In the vicinit7 ot Five Points, where pumping is to a great extent tram Sierran sands over,4ri.ng the Corcoran clay, water ot good quality is found. Total dissolved solids ot this water is about 1,000 ppnwith a sodium percentage of about 60.
In an area·along the valley trough ranging trom Mendota to Helm, mostq outside the service area, the Sierran sands over~g the Corcoran clq contain water ot high sodium chloride content. The sum of the determined constituents of this water averages about 5,(X)() ppm.
Lower zone.-The ground waters ot the lower zone are separated from the waters in the upper zone by the Corcoran cl.q' 1n most of the service area. Presentl.1' most ot the ground water pumped from the lower zone, some 85 percent or more ot the total pumpage, is a blend of deep zone native waters and water ot poorer quality from the upper zone via casing perforations or down through gravel envelopes.
27
Most ot the wells in the service area produce waters with total
determined constituents between 600 and 2,500 ppm. It is estimated
that under project conditions wells in the lower zone would continue
to produce water with average total dissolved solids ot 1,.200 ppm.
Native water, determined from wells without gravel packs and perforated only in the lower zone, is fair~ constant, generall,­being a sodium sulfate water with total determined constituents ot around 800 ppn.
Locally along the western margin of the service area, where the Corcoran clq is missing, ground water is high in calcium·and magnesium sultate sjmiJar to the upper zone. The total dissolved solids range from 1,000 ppn to as much as 3,000 ppm. This would suggest the possibility that there is some recharge from the surface. GROUND-WATER UTILIZATION
Ground-water Pumpage
GrO\Dld-water development began in the area about 1917 with the use ot deep ground-water supplies to irrigate orchards and vine7&l"ds. In the mid-thirties, it was realized that high salt-tolerant crops would succeed better than orchards and vineyards. Since this time the area has developed rapi~, especiall.1' since the mid-forties, with eJq>loitation ot ground water predominant:cy, tor cotton and grain crops.
The principal use or water in the service area is tor agricultural
•.
purposas·with veey minor amounts for domestic, farm.stead and industrial use. Most or this water has been derived from ground-water pumping. The Broadview, Panoche and San Luis Water districts now receive supplemental supplies from the Bureau's Delta-Mendota Canal.
For study purposes, the ground-water pumpage was estimated from Bureau or Reclamation unit farm delivel"Y' demand water requirements and using 1950 (Bureau)and 1958 (state ot <alitornia Department ot Water Resources) land use data. The average a.nnual ta.rm delivel"Y' demand (FDD) for the base period was derived from this dat·a by a straight line projection ot the 1950 and 1958 FDD. This, plus a V81"7 minor municipal use, amounted. to 725,000 acre-feet average annual gross demand for the base period. It has been estimated that
29
the Broadview, Panoche and San Luis water districts had an average
annual surface supply of about 28,000 acre-feet tor the base period.
Thus, the total ground-water pumpage is estimated to average 697,000
acre-feet per ,.ear tor the service area, ot which 485,000 acre-feet
represents pumpage in Westlands Water District.
Since wells in the service area draft on the upper and lower zones, determination ot pumpage trom each zone is dit.ficult to deter­mine. In U. s. G. s. Water-Supply Paper 1360-G it is stated: "A review ot the proportion ot perforated casing in the lower zone to that in the upper zone suggests that at least 75 percent and possibly more than SO percent ot the overall pumpage is from the lower zone." In this study it was estimated that 85 percent of the overall pumpage in the Westlands Water District (410,000 acre-feet) was pumped from the lower zone and that 90 percent was pumped from the lower zone in the area outside ot the Westlands Water District (190,000 acre­feet). The larger percentage was used tor the area outside of the Westlands Water District because fewer wells.in this area are per­forated in the upper zone.
Well Characteristics
Wells in the San Luis Service Area are drilled almost exclusively' b;r the rotary method. Bentonitic drilling mud is general.4' used to bring the cuttings to the surface and to prevent hole caving. The
30 casing is then lowered into the hole once it is drilled to its total
depth. ~ ot the deeper wells have been electric-logged to identify
potential water-bearing strata for casing perforations. Most wells
are 1.,000 to more than 2.,000 feet deep; well depths gener~ increase
westward. Wells of less than l.,000 feet are round a short distance
west or the valley trough. Yields vary areally but deep zone wells
average about 1,100 gallons per minute.
Wells in the service area are or three basic types: (l) those completed above the Corcoran clay; (2) those that penetrate the clay, and perforated onl¥ below the clay and so constructed that interzone exchange is not possible; and (3) those that penetrated the clay and so constructed (gravel pack and/or perforations) as to allow interzone exchange. The latter group is the most prevalent type.
A typical lower-zone well is generally 20 to 30 inches in diameter with casing 10 to 16 inches in diameter. Casing is usually-seamless steel 1/4 to 5/U, inch thick and butt-welded as it is put into the hole. Gravel, 1/4 inch or larger, is added to the annular space between the casing and hole. The casing is u~ 'li,-inch to about 200 feet below the water surface where it is reduced to 10 or 12-inch to reduce cost and increase velocities in the lower portion to prevent settling or sand. Perforations start either below the first reduction in casing size or below the Corcoran clay. The wells are developed by pumping or by surging with a swab.
31 Present Cost ot Pumping
Tables 1 and 2 present costs ot pumping based on average well sizes and production capacities tor lower-zone irrigation wells using 1960 equipment and power factors tor the Westland& Water District and tor the area outside the Westlands Water District but within the service area. Cost ot pumping as pro-rated on a total pumpage basis.in the two areas is about $13.15 per acre-foot. It must be remembered that these are present average costs and the actual range is large. Until such time as ground-water levels are stabilized., costs ot pumping will increase due to greater lifts.
32
,:.fA{t
-
.
-
Item
No. l. 2. 3. 4. 5. 6. 7. 8. 9. 10. ll. 12. 13. :u... 15. 16.
Item Description ·
1,100 1.,000 400 16 & l2 150 655,000 30,400 13,300 .43.,700 4,500 270 670 6,250 ll.,690 ll.69 .029
Well and pUMPINGData Pump capacity (gpn) Pump delivery (acre-feet/year) Pumping lift (feet) Well depth (feet)Casing diameter (inches) Pump motor lhp) Energy used (KWH/year) Well and equipment costs (dollars) Drilling, casing and development Pump, motor, etc., installed Total net investment Apnual cost (dollarsl Amortization (6% for 15 ;years) Taxes (2% of pump and motor costs) Maintenance (5% of ptDl'lP and motor costs) Energy-and standby charges -P.G. & E. Total annual costs (dollars) Cost/acre-toot Cost/acre-foot/foot lift
Table l.-Average Cost of Water from LOWER-ZONE
Irrigation Wells, 1960 Conditions
Westlands Water District
..
33
. .. ·
Table 2.-Average Cost or Water from lower-zone Irrigation Wells,1960 Conditions
Area outside ot Westlands Water District in San Luis Service Area
\
. C ('_Ar'/...,. A I ..
•. .
.34
No. =
Item Description
Well·and pumping data
1. 2. .3. 4. 5. 6.
Pump capacit7 (gpn) Pump delivel"T (acre-feet/year)Pumping lift (£eet) Well depth (feet) Casing diameter (inches) Pump motor (hp)
1,100 l,OCX) 600 2,000 16 & 12 250
7.
Energy used (KWH/year)
988.,000
Well and eguipnent costs (dollars)
8.
Drilling, casing and developnent
40,500
9. 10.
Pump, motor, etc., 1nstal1ed Total net investment
18,250 58,750
Annual cost (dollars)
ll. 12. 1.3. 14.
Amortization (6% tor 15 years) Taxes (2% ot pump and motor costs) Maintenance (5% ot pump and motor costs) Energy and standby charges -P.• G. & E. (t,--..;
6,050 365 910 9., 660 l
Total annual costs (dollars)
.:lo.,98f .·
.
15. 16.
Cost/acre-toot Cost/acre-toot/toot l:i£t
I , 4' ].6.99 .028 GROUND-WATER SUPPLY Present Conditions
General
The present annual replenishment of ground-water supplies in the San Luis Service Area is accomplished, in order or importance, by recharge presently being derived by the compaction of sediments in lower zone, by subsurface inflow to the lower zone from the east, by deep percolation from the gross demand, by interzone exchange from the upper zone to the lower zone, by percolation of stream flows from the west side, and by subsurface inflow to the upper zone from the east. No deep percolation from raintall was considered to occur. The various items or recharge have been estimated by a water supply inventory for the period 1950 through 1960. For water contract purposes, the ground-water study and ~sis of the service area was made tor the Westlands Water District and tor the area outside of the District. The inventory has been divided into.an upper zone ab~ve the Corcoran c~ and a lower zone below the c~. Table 3 shows the water supply inventory in the form o'r hydrologic equations for the two subareas and zones.
Increments
Compaction or lower-zone sed.iments.--During the base period the piezometric surface of the lower zone has declined about 10 feet per year. As a result, there has been an increased load on the lower zone sediments which has caused {l) a reduction of pore space in these
35
sed:lJnents thus releasing water for pumping, (2) land surface subsi­dence and its deleterious effect on surface utilities.
The quantity of water released by compaction has been estimated at .310,000 acre-feet per year for the base period. This quantity was considered to be equal to the surface subsidence time.a the acreage of the service area. Interagency subsidence maps show a weighted average of approximately 0.5-toot lowering of the land surface occurred per year. As water from this source is "mined" and irreplaceable, it represents an overdraft on the lower zone. Under project conditions the piezanetric surface will be at least stabilized and subsidence will be eliminated.
Lower-zone subsurface inflow from the east.-Subsurface inflow
.to this zone !l"Cln the east was based on~= TIL, using a coefficient of transmissibility (T) of 120,000 gallons per day per foot, and an average water level gradient (I) of 20 feet per mile determined from numerous tJ.s.o.s. ground-water maps for the period 1951 through 1960, and the length of section (L) ext.ends from near Stratford to a few miles northeast of Ora Loma, a distance of nearly 72 miles. The inflow section was divided into two segments; one 62-mile section from Stratford to northwest of Mendota for computing subinflow to Westlands Water District and another tor in.flow north of the District to the service area (See plate o). It was estimated from the equation Q = TIL that the estimated inflow to the service area averaged
37 190,0CX> acre-teet per year or which 160,000 was inflow to Westlands
Water District.
Transmissibility was based on a well recovery test conducted in 1920 near Westhaven and on two U.S.B.R. drawdown and recovery tests performed on wells 16/16-2 and 17/JJJ-5, as well as analyzing numerous utilit7 pump tests. Results of the Westhaven Test, a.na4'zed by' the u.s.G.s., and.U.s.B.R. tests indicate a coefficient of transmissibility ot 120,000 and 122,000 gallons per day per toot respectively. Although these tests are located on:cy, near the in.flow section, it is believed that due to the fairly constant specific capacities ot wells along the section, the transmissibility does not change significantly' between pumping tests sites. ·
Deep percolation from gross demand.--The farm delivery demand (FDD) is the quantity of water exclusive of effective precipitation required at the farm to grow a crop. This quantity includes econom.­c~ unavoidable farm losses, one of which is deep percolation of applied water. For purposes of this report it has been estimated that 17 percent ot the FDD would percolate below the root zone and would be a recharge to the upper zone. This study did not try to estimate losses of other very minor uses, but instead took 17 percent of the gross demand as deep percolation. This amounted to about 123,500 acre-feet per year for the base period•
.38 Interzone excha.nge.~Interzone exchange is possible because
at any given locality, water levels are always higher in the upper
zone than in the lower zone. In addition, lower-zone water quality
analyses shows that a portion of the lower zone's recharge is from
the upper zone. The present thought is that there is very little if
a?f3 water act~ moving through the Corcoran clay itsel.f, from
the upper zone to the lower zone. It is lalown that water is moving
down to the lower zone in well casings that are perforated in both
the upper zone and the lower zone, and thrOugh gravel packs.
The U. s. Geological Survey has made a series of velocity measurements of interzone flow using a deep-well Au current meter in unused irrigation wells. (Utilization of Ground-water Storage Capacity in the San Joaquin Valley, California; 1960 open file report). Down flow ot as much as l.l cfs was reported. They esti­mated from these measurements and the number of active and abandoned wells that the exchange through wells would be on the order of 100,000 acre-feet per year. No all.owanee was ma.de for flow through the gravel pack. In this study the interzone exchange figure was determined as the amount needed to balance the lower zone inventory for the base period and also amounts to 100,000 acre-feet per year. Thus, this quantity appears to be very reasonable as estimated by the two methods.
Percolation of west-side stream flows.~The pervious sediments of the Coast Range alluvial fans absorb the normal flows of west-side
.39 streams; however, during periods of high runoft sometimes stream
tlow reaches the valley t~gh. It has been estimated by the
Hydrology Branch in a previous Bureau report (1954) that 32,000
acre-feet of the normal annual flow percolates to ground water. Some
ll,000 acre-feet of this flow is assumed to be recharge to the upper
zone in the Westlands Water District with·the remainder, 21,000 acre­teet
percolating in the upper portion of the service area outside of
the District.
Uppet zone subsurface inflow from the east.-!ndications are that the upper zone has same subsurface in.flow f'rom the east. Ve17 little data are available at this time for this zone but in the u. s. G. s. Water-Supply' Paper 1360-G, it was estimated at 20,000 to 30,000 acre-feet _per year. In this study, 30,000 acre-feet per year was used for sub­i.ntlow above the Corcoran clay to Westlands Water District.
Undifferentiated recharge.--Exact balance in the base period inventory was not obtained but results were within general reasonable accuracy of other determined quantities. Thus, an item of 26,000 acre-feet was needed to balance the upper-zone inventory.
Gain in storage.--Comparison ot a 1952 generalized depth to water map (U. s. G. s. Water-Supp~ Paper 1469) to au. s. B. R.1962 map constructed from water level measurements in some 47 shallow power auger and drill holes indicates a rise in water levels of more than 40 feet. The 1952 map was constructed from water level measurements and
40
from electric logs and is of a generalized nature. It was, therefore, estimated on meager data that some 15,000 acre-feet ot water is going into upper-zone storage per year under base period conditions ot operation. When the present drilling program is complete and water­level trends have been determined after a period of years a more accurate estimate will be possible.
Decrements
Ground-water pumpage, lower zone.-Development of base period ground-water pumping quantities has been discussed previously in Ground-Water Utilization. The amount of pumpage that comes from the lower zone has been estimated to be 600,000 acre-feet per year for 1950 through·l960.
Ground-water pumpage, upper zone.--The remainder of the total pumpage comes from the upper zone and amounts to some 97,000 acre-feet per year.
Interzone exchange.-This is the same item as under increments, but since it comes trom the upper zone it is a decrement item to the upper zone.
Subsurface outtlow.~The service area does not have subsurface outflow. Hovever, for the base period, it was estimated that 10,000 acre-feet of subsurface outflow occurs from the Westlands Water District to the area outside of the District but within the service area.
41
Overdratt
An overdraf't occurs 1n an area when pumpage exceeds net recharge over a period ot years with the result water levels (upper zone) or the piezometric surface (lower zone) progressively' continue to decline. Only' meager data are available for the upper zone but.indications are that water levels are rising; therefore, an overdraft does not exist in the upper ~one. In the lower zone the piezometric surface has declined progressively about 100 feet over the base period and as a result, at the present time an undesirable source of recharge is taking place due to the compaction or lower-zone sediments. There­fore, this figure or 310,000 acre-feet per year constitutes overdraft.
Safe Ground-Water Suppg
Safe yield or ground-water supply of a ground-water reservoir is detined as the maximum reservoir draft which will not exceed net recharge, impair water quality, or cause pumping to become uneconomical. Ground-water quality is good in almost all or the lower zone and much of the upper zone except for the localities mentioned previously. Additional lowering of the ground-water levels of the lower zon~ if allowed to continue will induce further undesirable land surface subsidence. Present ground-water levels are within economi:c limits.
Sate ground-water supply or pumpage under present conditions of land use development is approximately 335,000 to 387,000 acre-feet depending upon whether it is assumed the undifferentiated item is a
42
desirable source of recharge or not. Excluding return seepage to ground water, the safe ground-water pumpage would be 226,000 to 27S,OOO acre-feet per ~ear.
43

Click tabs to swap between content that is broken into logical sections.

UNITED STATES DEPARTMENT OF THE INTERIOR
STEWARTL. UDALL, SECREI'ARY
********
BUREAU OF RECLAMATION FLOYD E. DOMINY, COMMISSIONER R. J. PAFFORD JR., REGIONAL DIRECTOR
REGION 2
********
SAN LUIS UNIT CENTRAL VALLEYPROJECT, CALIFORNIA
GEOLOGY AND GROUND-WATER RESOURCES DEFINITE PLAN APPENDIX
Sacramento, California
February 1963
. ' GEOLOGY AND GROUND-WATER RESOURCES SAN LUIS SERVICE AREA
The geology and ground-water studies were made and this appendix was prepared by the Regional Geology Branch, WilJ1am I. Gardner, Chief. This work was performed under the supervision ot Hibbarcl E. Richardson by William R. Cooke, assisted by Carl W. Roots, David c. Magleby and others ot the Geology Branch statt, both 1n the present study and in the earlier stages ot the geohydrological study ot the groand-water reservoir.
i
SAN WIS SERVICE AREA GlOOI.OGY AND GROUND-WATER RESOURCES • Definite Plan Appendix TABLE OF CONTENTS Pye No. Sl:JlllilARY • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • l INTROWC'?ION •••••••••••••••• •·• •••••••••••••••••••••••••• 7 Location and Extent •••••••••••••••••••••••••••••••••• 7 Acknowledgements••••••••••••••••••••••••••••••••••••• 8 General Description•••••••••••••••••••••••••••••••••• 8 Climate ••••••••••••••••••••••••••••••••••••••••••• 8 Phy-si.ograplJ¥ •••••••••••••••••••••••••••••••••••••• 8Soils·••••••••••••••••••••••••••••••••••••••••••••• 10 Basic Data ••••••••••••••••••••••••••••••••••••••••••• lOPrevious work ••••••••••••••••••••••••••••••••••••• 10 Ground-water records •••••••••••••••••••••••••••••• l3 Well-numbering s,rstem ••••••••••••••••••••••••••••• l4 Geologic Setting and History ••••••••••••••••••••••••• 15 GROUND-WATER G]!X)LOGY •••••••••••••••••••••••••••••••••••• 17 General •••••••••••••••••••••••••••••••••••••••••••••• 17 Upper Zone ••••••••••••••••••••••••••••••••••••••••••• 17 Corcoran Clay l8 Lower Zone ••••••••••••••••••••••••••••••••••••••••••• ··················~····················· 19 Nonwater-Bearing Formations •••••••••••••••••••••••••• 20 GROUND-WATER CONDITIONS ••••••••••••••••••••••••••••••••• 2l Source ••••••••••••••••••••••••••••••••••••••••••••••• 2l Occurrence ot Ground Water ••••••••••••••••••••••••••• 21 Upper zone •••••••••••••••••••••••••••••••••••••••• 2l Lower zone •••••••••••••••••••••••••••••••••••••••• 2l Depth and Movement ••••••••••••••••••••••••••••••••••• 22 Upper zone •••••••••••••••••••••••••••••••••••••••• 22 Lower zone •••••••••••••••••••••••••••••••••••••••• 2.3 Water-level Fluctuations ••••••••••••••••••••••••••••• 2.3 Upper zone •••••••••••••••••••••••••••••••••••••••• 2.3 Lower zone •••••••••••••••••••••••••••••••••••••••• 24 Qualit7 ot Ground Water•••••••••••••••••••••••••••••• 25 General ••••••••••••••••••••••••••••••••••••••••••• 25 Upper zone ·····················~·················· 25Lower zone •••••••••••••••••••••••••••••••••••••••• '2T
ii
CONTENTS (Cont.) Page No. GROUND-WATER UTILIZATION••••••••••••••••••••••••••••••• 29 Ground-Water Pumpage • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 29 Well Characteristics • • • •.• • • • • • • • • • • • • • • • • • • • • • • • • • • • 30 Present Cost ot Pumping••••••••••••••••••••••••••••• 32 GROOBD-WATER SUPPLY, Present Conditions.;.............. 35 General••••••••••••••••••••••••••••••••••••••••••••• 35 Increments•••••••••••••••••••••••••••••••••••••••••• 35 Compaction of lower-zone sediments••••••••••••••• 35 Lower-zone subsurface inflow trom the east....... 37 Deep percolation f'rom gross demand••••••••••••••• .38 Interzone exchange••••••••••••••••••••••••••••••• Percolation ot westside stream flows............. 39 .39 Upper-zone subsurface in.f'low .f'rom the east••••••• 40 Unditterentiated recharge•••••••••••••••••••••••• 40 Gain in storage•••••••••••••••••••••••••••••••••• 40 Decrements••••••••••••••••••••••••••••••••••••••••••· 41 Ground-water pumpage, lower zone••••••••••••••••• 41 Ground-waterpumpage, upper zone••••••••••••••••• 41 Interzone exchange••••••••••••••••••••••••••••••• 41 Subsurface outflow •••• ~•••••••••••••••••••••••··~ 41 Overdraft••••••••••••••••••••••••••••••••••••••••••• 42 Sate Ground-Water Suppl1' •••••••••••••••••••••••••••• 42 GROUND-WATER SUPPLY; Ultimate Project Conditions••••••• 44 General • • • • • • • • • • • • • • • • • • • • • • • • •.• • • • • • • • • • • • • • • • • • • • 44 Increments•••••••••••••••••••••••••••••••••••••••••• 44 Decrements•••••••••••••••••••••••••••••••••••••••••• 46 Ground-water pumpage, lower zone••••••••••••••••• 46 Ground-water pumpage, upper zone••••••••••••••••• 46 Outnow to drains................................ 46 Sate Ground-Water Suppll' •••••••••••••••••••••••••••• 47
iii SAN WIS SERVICE AREA TABJ.ES Table No• Page No. l. . Average cost ot water trom. lowe:r-sone irriga­tion wells, 1960 conditions-Westlands Water District•••••••••••••••••••••••••••• 33 2. Average cost ot water tram lower-sone irriga-tion wells, 1960 conditions-area outside ot Westland.a Water DJ.strict 1n the San Luis Service Area•••••••••••••••••••••••••••••• 34 Average annual water suppq inventor;y tor~ Luis Service Area-Period 1950 through 1960 Average annual water suppq inventor;y and sate ground-water suppq {pumpage)-ultimate project conditions•••••••••••••••••••••••· 45 PLATES Plate No. l. Ground-water contours-depth 1961 and change 1951-61, lower wate?'-bearing sone. 2. Location .map, u. s. B. R. drilling program, upper zone. Generalized e1evation and depth contours-top ot Corcoran clq. Ground-water profile A-A•. 5. Ground-water elevations, lower water-bearing zone, spring 1951. 6. . Ground-water elevations, lower ·water-bearing zone, spring 1961. 7. Water level hydrographs, upper zone. iv The service area of the San Luis Unit contains about 610,500 acres in the central-west side or the San Joaquin Valley, California (plate 1).
This ground-water report presents the physical and chemical characteristics of the ground-water reservoir and the estimates of safe ground.;.water supply (pumpage) for the service area. The purpose is to determine the average annual supplemental ~rt requirement frcm the San Luis Canal tor ultimate phases of developnent of the service area. For water contract purposes, the ground-water study and analTsea has been divided into two subareas; one for Westlands Water District and another for the area outside or the District. The ground-water reservoir has been divided into an upper zone above the Corcoran clay aquiclude and a lower zone below the clay. The sate ground-water supply (pumpage) under project conditions was determined on the basis ot a water supply inventoey £or the period 1950 through 1960 by eliminating an undesirable recharge item (water derived from canpaction or lower zone sediments), and r~by making an adjust­ment
for a greater amount of percolation due to a larger gross demand and project conveyance l~ases. The safe ground-water supply (pumpage) under project conditions is as follovs: Westlands
Outside of
Sate Ground-water
Water
Westlands
San Luis
Supply Cpumpage>
District
Water District (acre-feet}
Service Area
Lower zone Upper ~one
225,000§7.000
65,000 86.000
290,000173.000
TOTAL
312,000
151,000
46.3,000
Nearq all the local supply in the San Luis Service Area is from ground water and it will continue.to be important under project condi­tions. The ground-water reservoir is an accumulation or sediments or varying permeabilities and a maximum thiclmess or nearly .3,000 feet. The water-bearing sediments consist of coalescing alluvial ran deposits laid down by Coast Range streams and or sediments rrom the Sierra Nevada which were washed westerly beyond the present valley axis and are interlayered with the Coast Range alluvium to considerable depth beneath the valley-floor. The Coast Range type sediments are predomi­nantly fine-textured, ill-sorted, and yield less ground water than those from the Sierra Nevada which are mainly well sorted and coarser.
A relatively impervious layer called the Corcoran clay occurs at depths or 200 to 800 feet below the ground surface. '.!'his lake-bed deposit effectually divides the ground-water reservoir into two distinct parts--an upper water-bearing zone and a lower water-bearing zone. The upper water-bearing zone is ccmposed of Coast Range and Sierran sedi­ments with interconnected pervious beds and the ground water is uncon­fined to semiconfined, although some confinement has been noted in the
2
deeper Sierran sediments above the Corcoran cl.a)". Sierran-derived sediments below the Corcoran cla7 are major aquifers in geohydrologic continuit7 with aquifers underl1ing the east side of the San Joaquin Vallq. Water below the Corcoran cla7 in the lower water-bearing zone is under artesian head. Approximateq 85 to 90 percent of the total ground-water pumpage is estimated to now came from this deep zone.
Initialq, ground-water movement in both the upper and lower zones was eastward toward.a the vallq trough. At present, the semi.­perched water table, occurring over much of the service area, generalq has an eastward gradient. Water in the Sierran sands qing just above the Corcoran cla7 along the eastern boundar,' now has a westward gra­dient. In the lower zone increased pumpage, especialq since 1945, has reversed t_he gradient. During the base period (195~1960) ·the piesometric slope has averaged about 20 feet per mile toward the west along the eastern edge or the service area.
Depths to water range tran less than 10 feet tor the semiperched water table ot the upper sone to more than 700 feet to the piezanetric surface ot the lower zone (plate 1).
Upper zone semiperched water level measurements in recentq drilled Bureau teat holes indicate that the water table baa risen as much as 40 feet since 1952. Water levels in the lower portions ot the upper zone appear to be static or declining slightq. The average lower zone piezcmetric .surface dropped about 80 to 85 feet f'ran 1943 to 1951 and an additional 100 teet rrcm 1951 to 1961.
Upper zone water quality varies both laterally and vertica~. Water in the semiperched portion ot the upper zone is genera~ ot very poor quality with high total dissolved solids (TDS)•. Water quality improves with depth trom about 300 feet to the top or the Corcoran clay', averaging about 1,500 ppn total dissolved solids. However, sodium chloride waters averaging 5,000 ppn TDS occur in the basal portion ot the upper zone in an area mostq outside the service area along the trough frail Mendota to Helm. In the area around Five Points where heavy upper zone pumping occurs, water or 1,000 ppn TDS is found in the Sierran sands inmediateq overl1'ing the Corcoran clay. Native waters in the lover sone are f'airq constant, genera~.& sodium·sul­tate type with TDS ot about 800 ppn. However, very few wells produce water soleq !'rem the lower zone. Most of the wells in the service area yield a blend of' upper and lower zone waters with the total dissolved solids averaging 1,200 ppn.
All but minor amounts of' water used in the service area is derived frcm ground-wat~r pumpage and is estimated to be 697,0mplex]Jr folded and faulted Mesosoic and Tertiary strata. The Tertiary formations are elastic
15
strata_ot both continental and marine origin. The Mesozoic sedi­ments include great thicknessee or marine Cretaceous sandstone and shale, and variabq metamorphosed elastic and volcanic rocks or the Franciscan formation (Jurassic ? ) which rorma the core or the range.
The Cretaceous and the Tertiar;r marine formations which outcrop in the Coast Range underlie the valley at depth in a broad asyme­trical S1Dclinal told, whose steep limb is on the western side. During the late-Tertiary-, the Coast Range emerged as a high integrated land
C
mass, and the San Joaquin trough became, and has remained, an interior valley. In the late-Tertiary and Quaternary age, water-bearing conti­nental sediments were deposited on the expansive floor of the valley chiefq as alluvial ran and floodplain deposits, but aJ.so in lake beds during wetter periods. Some deformation in the Coast Range and bordering western part ot the valley has continued into Quaternary' so that the older continental Tertiary and Pleistocene beds are tilted and exposed in terraces and low foothills on the western edge or the valley.
'
.· .Lb
. GROUND-WATER GEOLOGY
General
The ground-water reservoir underlies the entire San Luis Service Area. The water-bearing sediments consist or both Coast Range and Sierra Nevada material. In this study the ground-water reservoir has been divided into an upper aone above the Corcoran cia,. aquiclude and a lower zone below the clay.
Upper ?.one
The upper zone includes sediments dawn to the Corcoran clay which are derived trm both the Coast Range and the Sierra Nevada. Thick­neaa ot this zone ranges to 800 feet (See plate .3). Surface deposits in the service area are Recent alluvial deposits derived primaril.7 trcm the Coast Range except tor a small portion alol}8 the eastern edge or the service area where Recent deposits of the Kings River occur. The upper sone sediments are Pleistocene and Recent 1n age.
Sierran sediments, consisting general.l1' of tine to medium well sorted sands and silts, extend up to nine miles west ot the eastern bound&r7 of the service ~a. These sediments are predom:lnantly fioodplain deposits ot the San Joaquin and Kings rivers which inter­finger with Coast Range material. This Sierran material is readily recognized by the abundance ot micaceous granitic fragments. The Sierran deposits exhibit a greater permeability than those of the
17
-
Coast Range. Since the source or these sediments are the Sierra Nevada, there is bydrologic continuity with aquifers to the east of the service area. There is also limited interconnaction with overlying Coast Range materials.
Irrigation wells completed in the upper zone Sierran deposits yield good quality of water to many wells along the eastern boundary or service area from north of Five Points to west of Lemoore. Average well yields are about l,000 gallons ·per minute. Elsewhere, many deep sone wells are perforated opposite the more permeable strata of the upper zone. From Mendota to Helm along tbe trough the micaceous sands in the upper zone contain water of inferior quality for irrigation.
The Coast Range alluvial deposits in the upper zone consist of highly lenticular beds of poorly sorted clay, silt and sand with an occasional bed or well-sorted sand and gravel. The coarser grained sediments occur on the higher portions ot the west-side fans. The Coast Range deposits are ot moderate permeability, generally recharged from west-side streams and by deep percolation of irrigation water. In some wells the Coast Range aquifer material of the upper zone is tapped by perforations in the well casing.
Corcoran Clay;
The Corcoran clay is a widespread body of diatomaceous clay and silt averaging 60 to 80 feet thick and found at depths to 800 feet. It underlies most of the service area. This clay, since it is
18
relatively impervious, has great hydrologic significance as it divides the gro,.md-water reservoir into two major zones, the confined lower zone and the unconfined or genera~ poorly confined upper zone. The Corcoran clay is believed to be Pleistocene in age and was formed in a great fresh water lake which covered much of the San Joaquin Valley. Ot.her workers believe it may be late Pliocene. Its structure and areal extent are shown on plate 3.
!e(er Zone
This zone is of great importance in the service area as it supplies an estimated 85 percent or more of the present ground-water pumpage. Aa mentioned above, it is effectively confined by the Corcoran cla:, except locally west or Huron. Much of the water now being produced from this zone is due to water released by compaction ot lower zone sediments. The base of the lower zone is not well defined but is considered to be the first occurrence of saline water. It is 1,000 to 3,000 feet below the ground surface. Maey deep wells in the service area perforate opposite the more permeable strata of the upper zone and in this manner, due to head differences, there is some intersone exchange between the upper and lower water bearing
zones.
Like the upper zone, sediments of this zone consist genera~ ot tine-grained Coast Range material inter.f'ingered with more permeable coarser grained granitic sands ot the Sierra Nevada. The latter
19
sediments yield most ot the ground water. Thus, again there is
lateral hydrologic continuity with Sierran materials to the east
as well as llmited vertical continuity between east and west-side
source materials.
Genera~, the lower sediments are referred to as the Tulare formation or Pliocene and Pleistocene age. The west-side Sierran sediments are.probab~ correlative with the east-side Kern and Friant formations.
Non-gter kring Fomations
The none-water bearing formations range in age from· Jurassic to Pliocene and underlie the ground-water reservoir. These formations outcrop in the foothill areas adjacent to the valley floor. The formations are large~ marine sandstones and shales containing poor quality or water. GROUND-WATER CONDITIONS
Source The source of ground water in the service area is at present
I
from water derived from the canpaction of sediments (subsidence),
subsurface inflow from the east and northeast from the percolation
or pumped ground water, and percolation from imported and natural
surface waters. All of these sources except percolation of pumped
ground water represent a supply' of new water to the area.
Rainfall in the area is of such low magnitude that recharge does not generally occur from this source.
Occurrence of Ground Water
Upper zone.-Ground water in the upper zone is found under various types of conditions, but in this report is grouped into two general types. The upper-most water in the service area is a semiperched water body. Below this semiperched body, but above the Corcoran clay, ground water is found in varying amounts ot confine­ment. In general, however, this zone is treated as being semiconfined and, thus, there is some degree of hydraulic interconnection of aquifers.
Lower zone.--The lower zone represents the ground-water reservoir below the Corcoran clay and is considered to be confined throughout the service area. However, locally west or Hllron where the Corcoran
21
clay is missing, there is some indication of recharge from the surface and thus, semiconfined conditions tor this portion of the service area are indicated.
Depth and Movement
· Upper zone.-The existence of a shallow, semiperched water table over the eastern half or the service area has been better defined by a recently conducted and partiall3' completed Bureau of Reclamation drilling program. Depth to this semi.perched body ranges from less than 10 feet near the eastern edge of the service area to more than 40 feet in the central part of the service area. Initially, all ground-water movement in upper and lower zones was from the west toward the valley trough to the east. The present gradient of the semiperched water table generall3' slopes toward the east; fran a northwest-southeast trending line approximatel.1' near the center of the service area the gradient appears to be westward. (See plate 2 and Drainage Appendix, plate 2.)
Geohydrologic data indicates that the water body existing in sands lying at depth above the Corcoran clay is semiconfined. In this zone thin beds of clay and silt impede vertical movement of water. Depths to water in aquifers above the clay are on the _order of 60 to 100 feet in the eastern portion of the service area; however, only a few wells of this type have been measured and control is poor. Meager water level measurements indicate the semiconfined water table
22
has a westward gradient in the Sierran sands along the eastern edge of the service area.
As mentioned previously, the Bureau drilling program will supple­ment existing upper zone data so that the relationship of ground-water bodies can be better interpreted.
Lower Zone.-Depth to the piezometric surface of the confined system below the Corcoran clay ranges from around 150 feet along the eastern edge or the service area to more than 700 feet in the western portion. Average depth to the piezometric surface in 1961 was about 400 feet. (See plate l.) Prior to World. War I, it is believed that the piezometric surface had a gently sloping, northeasterly gradient. Since that time, due to increasing ground-water draft on this zone, it now has induced a reversed gradient. Plate 4 shows the position of the piezometric surface for the years 1906, 1943, 1951, and 1961, and also the large magnitude of decline in piezometric surface as ground-water use has expanded. Elevation contours for the spring of 1951 (plate 5) and 1961 (plate 6) show ground-water movement to be toward the west at a gradient of about 20 feet per mile through thick Sierran aquifer :material. This has also been the average gradient for the last ten years along the eastern border of the service area.
Water-Level Fluctuations
Upper zone.-Long-term records are not available for water-level fluctuations in the upper zone. Indications of a rise in the semiperched
2.3 zone come from comparing recently drilled shallow Bureau holes, 1961 through 1963, with a generalized depth to water map presented in the u. s. G. s. Water-Supply Paper l.li.69, for the 1952 shallow water table. This map, although the best available, is o~ approxL­mate in many locations due to the lack or good control. At some locations apparent rises or five to more than 40 feet have been noted. These rises are apparently due to irrigation return flow •
.
Sane locations also indicate a lowering of the water table.
The piezometer pipes installed in the Bureau test hole l5/14-15E are good indicators or what is genera~ o_ccurring in the upper zone. Pipes were set within the following intervals; 0-280 feet, 300-460 feet, and 480-700 feet. The Oto 280-foot interval shows that water levels in this part of the upper zone have risen more than 20 feet since 1950. Interval 300 to 460 feet indicates that water levels have remained fairly stable except for seasonal fluctuations due to pumping. The 480 to 700-.foot water levels show a slight de­cline during the period of record and large magnitude or seasonal fluctuations which probably indicate nearby wells are tapping this zone. (See plate 7.)
Lower zone.--Lower-zone fluctuations of the piezometric sur­face are much better defined. In U. s. G. s. Water Supply Paper 398, plate 1 outlines an area of flowing artesian wells in the San Joaquin Valley for the year 1905. A portion of this outlined area is within ..
the service area. Since the end ot w·orld 'tlar I, the piezometric surface has declined due to greater and greater use of ground water for agriculture. Average elevations of the piezometric surface for a ntUnber of years have been determined from contour maps or the lower zone. The average elevation in the spring of 1943 of the service area was about 69 feet above sea level; by the spring of 1951, it had dropped to 13 feet below sea level. Water levels continued to decline and by 1961 they .had dropped to ll4 feet below sea level'or an average decline of about 10 feet per year. Wells in western portion of the service area have been declining on the order of 15 feet per year. Pl.ate l shows lines of equal change of the piezometric surface of the lower zone for the period 1951 through 1961.
9Balit;t of Ground Water
General.~Most ot the irrigation wells 1n the service area are perforated 1n the upper and lower zones and the chemical nature of water from a given well depends upon its perforated interval. The character of water in the upper and lower zones is described in some detail in the U. s. G. s. Water Supply Paper l,360-G. The Bureau has obtained considerable data in the past year primarily for the shallow portion of the upper zone.
Upper zone.-Ground waters in this zone contain high concentra­tions of sulfate salts. Chemical changes in the upper-zone waters occur latterall.y such as along the eastern portion of the area where
25
waters from the eastside and westside commingle; gradational changes al30 occur with increasing depth.
Chemical analy'ses of water samples taken from Bureau holes drilled to a few feet below the water table, generally in the eastern half or the service area and within 75 feet or the ground surface, indicate that north of Bureau holes 807, 806, and 821 and south of holes 827, 828, and 829, the waters are generally of the sodium sulfate type (See plate 2). The area between these holes has water of the calcium-magnesium-sulfate type. The Drainage Appendix presents the chemical analy'ses or water from these shallow holes and sane from deeper holes in the upper zone drilled thus far. The total dissolved solids (TDS), of these waters less than 75 feet deep, ranges from 1,145 parts per million (PJ:!ll) to 51,250 ppn, averaging around 12,000 pt:m, with the sodium percentage ranging from 20 to 90. From the limited deeper holes, completed ·to date, it appears that the water quality improves with depth. Water quality from 75 to 200 or .300 feet below the land surface is still a rather moot question. The U.S. G. So in Water-Supply Paper l.360-G, .frail rather limited data, reports
most or the waters in the upper 200 to .300 feet are of the calcium and magnesium sulfate type with the sum of the determine constituents averaging about .3,000 ppn with a sodium percentage or .35 •. From this, it appears that the water below 75 feet is of better quality. The water of poor quali~y in the eastern half or the service area within 75 feet of ground surface presents, serious threat to the ground-water
26
--:
supply above the Corcoran clq under present conditions ot operation. Under project oonditiona with drains over the lower halt ot the service area and water ot ver17 good qualit7 being imported, water quality will improve in this part of the upper zone.
The chemical character ot the water in the upper zone trom 200 to 300 teet below land surface to the Corcoran c~ shows consider­able lateral variance. These waters show a decrease in total deter­mined constituents to about 1,500 ppm and an increase in sodium to about 55 percent. In the vicinit7 ot Five Points, where pumping is to a great extent tram Sierran sands over,4ri.ng the Corcoran clay, water ot good quality is found. Total dissolved solids ot this water is about 1,000 ppnwith a sodium percentage of about 60.
In an area·along the valley trough ranging trom Mendota to Helm, mostq outside the service area, the Sierran sands over~g the Corcoran clq contain water ot high sodium chloride content. The sum of the determined constituents of this water averages about 5,(X)() ppm.
Lower zone.-The ground waters ot the lower zone are separated from the waters in the upper zone by the Corcoran cl.q' 1n most of the service area. Presentl.1' most ot the ground water pumped from the lower zone, some 85 percent or more ot the total pumpage, is a blend of deep zone native waters and water ot poorer quality from the upper zone via casing perforations or down through gravel envelopes.
27
Most ot the wells in the service area produce waters with total
determined constituents between 600 and 2,500 ppm. It is estimated
that under project conditions wells in the lower zone would continue
to produce water with average total dissolved solids ot 1,.200 ppm.
Native water, determined from wells without gravel packs and perforated only in the lower zone, is fair~ constant, generall,­being a sodium sulfate water with total determined constituents ot around 800 ppn.
Locally along the western margin of the service area, where the Corcoran clq is missing, ground water is high in calcium·and magnesium sultate sjmiJar to the upper zone. The total dissolved solids range from 1,000 ppn to as much as 3,000 ppm. This would suggest the possibility that there is some recharge from the surface. GROUND-WATER UTILIZATION
Ground-water Pumpage
GrO\Dld-water development began in the area about 1917 with the use ot deep ground-water supplies to irrigate orchards and vine7&l"ds. In the mid-thirties, it was realized that high salt-tolerant crops would succeed better than orchards and vineyards. Since this time the area has developed rapi~, especiall.1' since the mid-forties, with eJq>loitation ot ground water predominant:cy, tor cotton and grain crops.
The principal use or water in the service area is tor agricultural
•.
purposas·with veey minor amounts for domestic, farm.stead and industrial use. Most or this water has been derived from ground-water pumping. The Broadview, Panoche and San Luis Water districts now receive supplemental supplies from the Bureau's Delta-Mendota Canal.
For study purposes, the ground-water pumpage was estimated from Bureau or Reclamation unit farm delivel"Y' demand water requirements and using 1950 (Bureau)and 1958 (state ot acre-teet per year or which 160,000 was inflow to Westlands
Water District.
Transmissibility was based on a well recovery test conducted in 1920 near Westhaven and on two U.S.B.R. drawdown and recovery tests performed on wells 16/16-2 and 17/JJJ-5, as well as analyzing numerous utilit7 pump tests. Results of the Westhaven Test, a.na4'zed by' the u.s.G.s., and.U.s.B.R. tests indicate a coefficient of transmissibility ot 120,000 and 122,000 gallons per day per toot respectively. Although these tests are located on:cy, near the in.flow section, it is believed that due to the fairly constant specific capacities ot wells along the section, the transmissibility does not change significantly' between pumping tests sites. ·
Deep percolation from gross demand.--The farm delivery demand (FDD) is the quantity of water exclusive of effective precipitation required at the farm to grow a crop. This quantity includes econom.­c~ unavoidable farm losses, one of which is deep percolation of applied water. For purposes of this report it has been estimated that 17 percent ot the FDD would percolate below the root zone and would be a recharge to the upper zone. This study did not try to estimate losses of other very minor uses, but instead took 17 percent of the gross demand as deep percolation. This amounted to about 123,500 acre-feet per year for the base period•
.38 Interzone excha.nge.~Interzone exchange is possible because
at any given locality, water levels are always higher in the upper
zone than in the lower zone. In addition, lower-zone water quality
analyses shows that a portion of the lower zone's recharge is from
the upper zone. The present thought is that there is very little if
a?f3 water act~ moving through the Corcoran clay itsel.f, from
the upper zone to the lower zone. It is lalown that water is moving
down to the lower zone in well casings that are perforated in both
the upper zone and the lower zone, and thrOugh gravel packs.
The U. s. Geological Survey has made a series of velocity measurements of interzone flow using a deep-well Au current meter in unused irrigation wells. (Utilization of Ground-water Storage Capacity in the San Joaquin Valley, California; 1960 open file report). Down flow ot as much as l.l cfs was reported. They esti­mated from these measurements and the number of active and abandoned wells that the exchange through wells would be on the order of 100,000 acre-feet per year. No all.owanee was ma.de for flow through the gravel pack. In this study the interzone exchange figure was determined as the amount needed to balance the lower zone inventory for the base period and also amounts to 100,000 acre-feet per year. Thus, this quantity appears to be very reasonable as estimated by the two methods.
Percolation of west-side stream flows.~The pervious sediments of the Coast Range alluvial fans absorb the normal flows of west-side
.39 streams; however, during periods of high runoft sometimes stream
tlow reaches the valley t~gh. It has been estimated by the
Hydrology Branch in a previous Bureau report (1954) that 32,000
acre-feet of the normal annual flow percolates to ground water. Some
ll,000 acre-feet of this flow is assumed to be recharge to the upper
zone in the Westlands Water District with·the remainder, 21,000 acre­teet
percolating in the upper portion of the service area outside of
the District.
Uppet zone subsurface inflow from the east.-!ndications are that the upper zone has same subsurface in.flow f'rom the east. Ve17 little data are available at this time for this zone but in the u. s. G. s. Water-Supply' Paper 1360-G, it was estimated at 20,000 to 30,000 acre-feet _per year. In this study, 30,000 acre-feet per year was used for sub­i.ntlow above the Corcoran clay to Westlands Water District.
Undifferentiated recharge.--Exact balance in the base period inventory was not obtained but results were within general reasonable accuracy of other determined quantities. Thus, an item of 26,000 acre-feet was needed to balance the upper-zone inventory.
Gain in storage.--Comparison ot a 1952 generalized depth to water map (U. s. G. s. Water-Supp~ Paper 1469) to au. s. B. R.1962 map constructed from water level measurements in some 47 shallow power auger and drill holes indicates a rise in water levels of more than 40 feet. The 1952 map was constructed from water level measurements and
40
from electric logs and is of a generalized nature. It was, therefore, estimated on meager data that some 15,000 acre-feet ot water is going into upper-zone storage per year under base period conditions ot operation. When the present drilling program is complete and water­level trends have been determined after a period of years a more accurate estimate will be possible.
Decrements
Ground-water pumpage, lower zone.-Development of base period ground-water pumping quantities has been discussed previously in Ground-Water Utilization. The amount of pumpage that comes from the lower zone has been estimated to be 600,000 acre-feet per year for 1950 through·l960.
Ground-water pumpage, upper zone.--The remainder of the total pumpage comes from the upper zone and amounts to some 97,000 acre-feet per year.
Interzone exchange.-This is the same item as under increments, but since it comes trom the upper zone it is a decrement item to the upper zone.
Subsurface outtlow.~The service area does not have subsurface outflow. Hovever, for the base period, it was estimated that 10,000 acre-feet of subsurface outflow occurs from the Westlands Water District to the area outside of the District but within the service area.
41
Overdratt
An overdraf't occurs 1n an area when pumpage exceeds net recharge over a period ot years with the result water levels (upper zone) or the piezometric surface (lower zone) progressively' continue to decline. Only' meager data are available for the upper zone but.indications are that water levels are rising; therefore, an overdraft does not exist in the upper ~one. In the lower zone the piezometric surface has declined progressively about 100 feet over the base period and as a result, at the present time an undesirable source of recharge is taking place due to the compaction or lower-zone sediments. There­fore, this figure or 310,000 acre-feet per year constitutes overdraft.
Safe Ground-Water Suppg
Safe yield or ground-water supply of a ground-water reservoir is detined as the maximum reservoir draft which will not exceed net recharge, impair water quality, or cause pumping to become uneconomical. Ground-water quality is good in almost all or the lower zone and much of the upper zone except for the localities mentioned previously. Additional lowering of the ground-water levels of the lower zon~ if allowed to continue will induce further undesirable land surface subsidence. Present ground-water levels are within economi:c limits.
Sate ground-water supply or pumpage under present conditions of land use development is approximately 335,000 to 387,000 acre-feet depending upon whether it is assumed the undifferentiated item is a
42
desirable source of recharge or not. Excluding return seepage to ground water, the safe ground-water pumpage would be 226,000 to 27S,OOO acre-feet per ~ear.
43